Summary of interview conducted on 14. september 2001
at Aarhus Universitet, by Arne Hessenbruch
- Early history of surface science
The beginnings of STM research at Aarhus University (1986-1989)
- 1960s: The US space program boosted surface science in the 1960s
by developing oil-free ion pumps and a new ultra-high vacuum technology
based on stainless steel chambers, replacing the older glass chambers
and mercury pumps. This greatly facilitated the use of a host of sensitive
measurement techniques, especially low-energy electron diffraction
(LEED) and Auger spectroscopy. As a result, surface science expanded
exponentially in the 1970s and '80s.
- 1980s: The arrival of the Scanning Tunneling Microscope improved
not just the resolution to the atomic level, but it also enabled temporal
measurements illustrating dynamic effects on the surface. It directly
eliminated some theories of surface phenomena and has helped to build
up a new conceptual framework for surface science. Prior to the advent
of STM, LEED studies dominated surface science conferences; now they
have become a small minority.
Development of STM theory and difficulties of interpretation
- Besenbacher and Ivan Stensgaard had a background in metal surface
analysis using ion scattering. In 1986, the use of laser technology
seemed unsatisfactory because it yielded only integral information
about diffusion on surfaces, whereas the steadily improving STM
promised atomic resolution and local information about diffusion.
Besenbacher aimed early for information about dynamics of surface
- Resources drawn upon included a well-staffed in-house workshop,
funding for both research time and equipment, materials loaned from
locally available apparatus (e.g. piezo elements used to direct
laser mirrors), and publications (especially Binnig & Rohrer's).
Building an STM for ambient use turned out to be quite straightforward.
- The group then turned to the more challenging task of building
one for use in UHV. Here different materials were required, partly
because the chamber needs to be baked out before use. Resources
for this UHV-STM included an idea for an inchworm motor by Burleigh
Instruments. The UHV-STM was tested on the Si 7x7 reconstruction
the atomic resolution image of which had been established by September
1989 as a yardstick (Besenbacher's group digressed into semiconductors
in this period due to Klaus Mortensen, a post-doc who had spent
a year with Gene Golovchenko at Harvard).
- Outside contacts included Golovchenko, Jürgen Behm, and two
students at the Danish Technical University (who in turn had connections
to Chalmers University in Gothenburg, Sweden, and Kim Carneiro at
the Danish Institute for Fundamental Metrology).
Center for Atomic-scale Materials Physics (1993-)
- STM images result from a convolution of the electronic and geometric
surface structure with that of the tip. STM theory utilizes first-order
perturbation theory. The interpretation of STM images requires both
understanding of the theory and experience, particularly because
the tip structure might change during the measurement. Measuring
requires patience because the desirable tip structure might suddenly
come into being.
- The development of STM theory has depended heavily on the improvement
in computer capacity. The conceptual apparatus of the tunneling
theory has changed little: perturbation theory applied to the Hamiltonian
with the the tip approximated as an s-wave. The theory for the calculation
of surface electronic structure has become known as density function
- Tip preparation still difficult making replication difficult too.
New projects: biocompatibility and fuel cells
- CAMP was started in 1993 with funding from Danmarks Grundforskningsfond,
a funding program fostering a few "elite" research centers.
This enabled the gathering of a critical mass of researchers, including
many on the PhD and post-doc level. Elite funding was an innovation
within Danish research traditions by the centre-right government of
Poul Schlüter and, despite its initial opposition, the social
democratic government (1992-2001) warmed to it.
- Close collaboration between a theoretical group at Denmark's Technical
University and Besenbacher's experimental one at the University of
Aarhus turned out fruitful. The close personal relationship between
the two center heads (Jens Nørskov and Besenbacher) mattered
greatly. To this day they communicate several times daily. Mutual
enrichment has been exemplary, and other centers have modeled themselves
- One of CAMP's main achievements has been films of movement on metal
surfaces in real time. Another has been the design of catalyst surfaces
with desirable properties.
- CAMP has analysed the surface activity of a catalyst used in "steam
reforming" for hydrogen production. Scanning probe microscopy
methods can be used to design catalysts with desirable qualities.
There is a collaboration with the company of Haldor Topsøe,
an important supplier of catalysts for ammonium synthesis. This involves
contacts, shared research, and Topsøe funding a post-doc position.
- Linear model (from pure science to application) no longer applicable.
Long-term government funding (e.g. 20 years) still desirable, but
the separation of institutions doing separate research on pure and
applied science non-sensical. Research in the style of Pasteur (basic
but simultaneously with a keen eye to application - the reference
is to Donald E. Stokes, Pasteur's Quadrant - Basic Science and
Technological Innovation, Washington, D.C.: Brookings Institute
Press, 1997) is feasible, and CAMP's form of research resembles that
of Pasteur. There has been a general shift away from thinking in terms
of pure and applied. Funding by private companies is no longer seen
as suspect and the next generation is barely aware that such funding
used to be scorned.
A Danish equivalent of the National Nanotechnology Initiative?
- Just as it is important for companies to diversify (as the case
of Lego reveals), so scientific centres should too. When Hans Jørgen
Pedersen, a research director at Danfoss and a member of the faculty
board) suggested investigating the possible contributions of scanning
probe microscopy (SPM) to biocompatibility research, Besenbacher jumped
at the opportunity.
- It was possible to raise money earmarked for interdisciplinary research
and with it to employ two post-docs and a couple of students.
- New skills have to be developed. Biocompatibility requires investigations
of the liquid-solid interface which is in many ways different from
research on solid-vacuum interfaces. But the core skills acquired
over years with SPM will help substantially nonetheless.
- Activities are afoot within Danish government ministries to earmark
a part of the budget for a Danish equivalent of the National Nanotechnology
Initiative. [However, routine budget negotiations were disrupted by
November 2001's elections resulting in a change in government from
social democrats to a centre-right coalition.]
- CAMP has not been in the habit of taking out patents, but there
is no reason why this should not change, especially with collaboration
on biocompatibility. Colleagues in molecular biology already have
much experience with patents. Aarhus University does not put pressure
on researchers to apply for patents, though.